The present invention relates to a marking method of forming a mark on a photosensitive material in which the mark can be confirmed on an undeveloped state or developed state of the photosensitive material. Especially, the present invention relates to a marking method preferably usable to record a mark on a photosensitive film which is used for a hard copy apparatus such as a CT scanner by which accuracy image such as medical diagnosis images needing high flatness are formed on the photosensitive film.
Conventionally, when the name of a maker, a kind of a film, an effective usable period, a lot No. are marked on a photosensitive material such as a X-ray film, since it is necessary to confirm the marks on the undeveloped state of the photosensitive material due to the convenience on the handling, by pressing printing types onto the photosensitive material, fogs and deformation in the form of the printing types are caused by the pressure on the surface of the photosensitive material so that the marks are formed.
However, the abovementioned marking method with the use of the printing types has the following problems.
(1) Printing type exchange is necessary in the time of changing a marking pattern, exchange time is long, and it is difficult to conduct instant printing type exchange and to set the printing type in a production line. PA1 (2) Adjustment of pressure balance between printing types by the height of each printing type is difficult and long time is needed for the adjustment. Further, sine it is necessary to conduct the adjustment work in a dark room, the working condition is very bad. PA1 (3) The printing types are expensive and the appointed date of delivery is long. When the new kind of a photosensitive film is developed, preparation period is necessary. PA1 (4) Since film base surface becomes uneven by the printing types, when an image is photographed, the image may become out of focus on the uneven film. Accordingly, it is difficult to conduct the printing types on an image recording film, especially, on a film used for a hard copy of a high precision image in a CT scanner. Because the film for CRT is required to have a high flatness. PA1 driving a plurality of laser beam sources On or Off independently; PA1 irradiating the photosensitive material with a laser beam from each laser beam source under a condition that relationship between energy density E (unit: w/cm.sup.2) and a pulse width S (unit: seconds) locates within a region enclosed by formulas described below, whereby forming dots in a form of approximately circle with a predetermined interval. EQU log E=k log S+m.sub.1 EQU log E=k log S+m.sub.2 EQU log S=log 3-5 EQU log S=log 2-4 PA1 wherein k=0.46 PA1 m.sub.1 =3.68 m.sub.2 =2.92 PA1 driving a plurality of laser beam sources On or Off independently; PA1 irradiating the photosensitive material with a laser beam from each laser beam source under a condition that relationship between energy density E (unit: w/cm.sup.2) and a pulse width S (unit: seconds) locates within a region enclosed by formulas described below, whereby forming dots in a form of approximately circle with a predetermined interval. EQU log E=k log S+m.sub.3 EQU log E=k log S+m.sub.4 EQU log S=log 3-5 EQU log S=log 2-4 PA1 wherein k=0.46 PA1 m.sub.1 =3.23 m.sub.2 =3.11 PA1 driving a laser beam source On or Off independently; PA1 irradiating the photosensitive material with a laser beam from the laser beam source under a condition that relationship between energy density E (unit: w/cm.sup.2) and a pulse width S (unit: seconds) locates within a region enclosed by formulas described below, whereby forming dots in a form of approximately circle with a predetermined interval. EQU log E=k log S+m.sub.1 EQU log E=k log S+m.sub.2 EQU log S=log 3-5 EQU log S=log 2-4 PA1 wherein k=0.46 PA1 m.sub.1 =3.68 m.sub.2 =2.92 PA1 driving a laser beam source On or Off independently; PA1 irradiating the photosensitive material with a laser beam from the laser beam source under a condition that relationship between energy density E (unit: w/cm.sup.2) and a pulse width S (unit: seconds) locates within a region enclosed by formulas described below, whereby forming dots in a form of approximately circle with a predetermined interval. EQU log E=k log S+m.sub.1 EQU log E=k log S+m.sub.2 EQU log S=log 3-5 EQU log S=log 2-4 PA1 wherein k=0.46 PA1 m.sub.3 =3.23 m.sub.4 =3.11
Therefore, under the present situation, the marking is not conducted by the printing types for the film that high flatness is required. As a result, there is an inconvenience that it is difficult to identify the film. Further, in accordance with P.L. (production liability) law, it is necessary to conduct marking production information on a film. However, it is difficult to follow the P.L. law.
A mark is exposed on a film with a laser beam by a laser beam printer. In this case, the mark can not be visually confirmed before development.
Although a mark formed by thermal fog with laser beam is tried recently, there is a problem that when dust stick to the film surface, a spark occurs and harmful fog is caused in the vicinity of the mark on the film by the spark.
In order to solve such problems, the present inventors consider to conduct a marking by the use of dot printing type laser marker that can program printing pattern and examine its utility. As a result, the following problems has been found.
That is, as shown in a side view of FIG. 5, generally a polygon mirror 4 is used for scanning of laser beam. In this case, since a laser beam scans at high speed on a film, a dot of the laser beam is extended in a form of an oval in the main scanning direction as shown in FIGS. 6(a), 6(b) and 6(c). Accordingly, in a line component (vertical line) in the main scanning direction, dots are superimposed with each others and the laser beam irradiation time period on the superimposed portion is increased. As a result, since the density value of black on the line component in the main scanning direction becomes darker than that of the line component in the sub-scanning direction or the slanted line in which dots are not superimposed, density irregularities takes place on the marked character.
The increase of the laser beam irradiation time period by the partial superimposition among dots may have a risk to cause abnormal combustion when foreign material such as dust sticking on the film surface resides on the photosensitive film. In this case, spark generated by the abnormal combustion cause abnormal fog on the photosensitive film. In order to avoid the above problem, spacing means such as a skip font is tried to use so as to space between dots in the main scanning direction as shown in FIGS. 6(d), 6(e) and 6(f). However, the configuration of the character is not balanced.